Heat Exchanger with an All-Metal Construction, in Particular an All-Aluminium Construction

ABSTRACT

The invention relates to a heat exchanger with an all-metal construction, preferably an all aluminium construction. Said heat exchanger comprises a network ( 2 ) of ribs and tubes ( 4 ), the ends ( 4   a ) of the layer having and enlarged rectangular form, longitudinal and narrow sides and at least one U-profile ( 6 ) with collection chambers ( 3 ) that comprise lateral limbs ( 6   a   , 6   b ). The longitudinal sides ( 4   b ) are connected to one another and the narrow sides ( 7   a   , 7   b ) to the limbs ( 6   a   , 6   b ) of the U-profile ( 6 ) by a numeral union, preferably by means of soldering. According to the invention, the U-profile ( 6 ) is optimised for tension.

The invention relates to a heat exchanger with an all metal, preferably all aluminum, construction, in particular as claimed in the preamble of patent claim 1.

All metal heat exchanger, in particular soldered aluminum heat exchangers, are used as coolant radiators or charger radiators for motor vehicles. The advantage of these heat exchangers is that they are of one grade of material and therefore can easily be recycled. DE-A 195 43 986 by the applicant has also disclosed a soldered aluminum heat exchanger with flat tubes whose ends are widened to form a rectangular cross section. The tube ends have longitudinal sides and narrow sides, with the longitudinal sides resting one against the other in a sealed fashion and being soldered to one another, while the narrow sides form external surfaces which are connected to the internal surfaces of a collecting box. The collecting box has an approximately U shaped profile (U profile) with lateral limbs which embrace the narrow sides of the tubes. This design allows a conventional tube bottom with the corresponding tube/tube bottom connections to be dispensed with. As an alternative to the U profile, this document also discloses a cylindrical collecting vessel which has parallel collars for abutting against the narrow sides of the tube ends. A problem with this design is the soldered connections when internal pressure is applied to the heat exchanger during operation. In particular in the region of the soldered connections between the narrow sides of the tube ends and the limbs of the collecting box it is possible for fractures to form in the soldering seam, in particular if the collecting box profile is not resilient and flexural stresses additionally occur in the region of the soldering seam.

The object of the present invention is to improve the durability of the soldered connections, in particular in the region of the tube ends, in a heat exchanger of the type mentioned at the beginning.

This object is achieved by means of the features of patent claim 1. The invention provides that the U profile of the collecting box be embodied in a way which is optimized with respect to stress, the configuration according to the invention providing a round arc between two straight limbs of the U profile. At the same, the limbs preferably merge with a continuously increasing curvature into the round arc which has an upper, symmetrically arranged apex point. This configuration results in favorable distribution of stress in the cross sections of the collecting box because the profile of the collecting box can yield owing to the arcuate design. As a result, unfavorable flexural stresses can also be kept away from the soldered connections. Overall, this optimized profile configuration produces a durable soldered connection with which the formation of fractures as a result of unfavorable loading is avoided.

In one advantageous exemplary embodiment of the invention, irregularity in the loading, such as force, at the junction from one material thickness to another material thickness is reduced or prevented.

An exemplary embodiment of the invention is illustrated in the drawing and, will be described in more detail below. In the drawing:

FIG. 1 shows a detail of an all aluminum radiator with a collecting box, and

FIG. 2 shows a cross section through the collecting box.

FIG. 1 shows a detail of an all aluminum coolant radiator 1 such as is used in particular for motor vehicles. The coolant radiator 1 can be embodied as a downdraft radiator or a cross flow radiator—the exemplary embodiment shows a cross flow radiator with a network 2 and a laterally arranged collecting or coolant box 3. The network 2 is composed of horizontally arranged flat tubes 4 between which only partially illustrated corrugated ribs 5 are arranged. The tubes 4 have tube ends 4 a which are widened to form a rectangular cross section (not illustrated) and bear one against the other with their longitudinal sides. This design is known from DE-A 195 43 986 which is mentioned at the beginning and which is included in its entirety in the disclosure contents of this application. All the parts of the coolant radiator 1, that is to say flat tubes 4, corrugated ribs 5 and collecting box 3 are composed of aluminum or aluminum alloys or metal or metal alloys and are connected to one another by hard soldering.

FIG. 2 shows a cross section through the collecting box 3 which has a U shaped cross sectional profile 6 with two limbs 6 a, 6 b and a round arc 6 c which connects the two limbs 6 a, 6 b. The open region of the U profile 6 embraces one tube end 4 a of the flat tube 4. As mentioned, the flat tube ends 4 a are widened to form a rectangular cross section, the longitudinal side 4 b of which can be seen in FIG. 2, i.e. is in the plane of the drawing. The narrow sides, which are soldered to the inside of the limbs 6 a, 6 b, extend perpendicularly to this longitudinal side 4 b, while the longitudinal sides 4 b of adjacent tubes 4 are soldered directly to one another. The U profile 6 has a width B and a height H, with H being greater than B, preferably a multiple of 1.75. The limbs 6 a, 6 b extend from the longitudinal sides 4 b, firstly in parallel and then increasingly assume a convergent direction which merges into the round arc 6 c. The profile 6 is of symmetrical design to the center line which passes through the round arc 6 c at an apex point 6 d. To this extent, the two limbs 6 a, 6 b merge with increasing curvature into the round arc 6 c, it being possible for this round arc 6 c to be made parabolic, ellipsoidal or circular. The increase in curvature of the U profile 6 in conjunction with the relatively large height H has the effect that when internal pressure is applied, represented by arrows P, a favorable, essentially tensile stress profile is produced in the cross sections of the U profile 6, which is preferably bent out of a piece of sheet metal. As already mentioned, the U profile 6 is soldered to the tube ends 4 a by means of its limbs 6 a, 6 b, specifically by means of the solder faces 7 a, 7 b. Owing to the previously described configuration of the U profile 6, the solder faces 7 a, 7 b are very largely freed of flexural stresses since the U profile 6 can deform elastically, in particular in its upper region, i.e. in the region of the round arc 6 c. As a result, the soldered connections 7 a, 7 b are subject to less critical stressing, as a result of which fracture formation is also avoided.

The boxes and side parts form a stable frame so that the configuration in the manner of a round arc alleviates the operationally induced thermal stresses by displacing them in the direction of the tube ends. 

1. A heat exchanger with an all metal, preferably an all aluminium, construction, comprising a network of ribs and tubes with tube ends which are widened in rectangular shapes and have longitudinal and narrow sides, and comprising at least one collecting box which has a U profile with lateral limbs, the longitudinal sides being connected to one another, and the narrow sides being connected to the limbs of the U profile, in a materially joined fashion, preferably by means of soldering, wherein the U profile is embodied in an optimized fashion in terms of stress.
 2. The heat exchanger as claimed in claim 1, wherein the limbs of the U profile are of straight design in the region of the narrow sides and merge continuously into a round arc.
 3. The heat exchanger as claimed in claim 2, wherein the limbs merge, with a continuously increasing curvature, into the round arc which reaches its maximum curvature at an apex point.
 4. The heat exchanger as claimed in claim 3, wherein the U profile is of symmetrical or asymmetrical design with respect to a center line M which runs through the longitudinal side of the tube ends.
 5. The heat exchanger as claimed in claim 1, wherein the U profile has a height H and a width B where H>B, preferably 1.5 B H 2.0 B. 